1. Technical Field
The present invention concerns the field of semiconductor components. More particularly, the present invention concerns a silicon-based light-emitting semiconductor component and a process for the production of such a light-emitting semiconductor component.
2. Discussion of Related Art
The development in semiconductor technology is going in the direction of higher integration density of integrated circuits and faster signal processing. Therefore future integrated circuits will probably no longer be based solely on electronic signal production and signal processing, but will increasingly integrate optical and optoelectronic components in order to achieve a further increase in the processing speed and a reduction in the power loss. A further endeavor is to reduce the architectonic complexity by multiplexing of optical signals in waveguides on the chip. Infrared spectral ranges are predestined for optical signal processing.
The base material of semiconductor technology is silicon. Known efficient light-emitting and laser diodes in the infrared spectral range however are not made from silicon but in particular from III-V-semiconductors such as gallium arsenide, indium arsenide or indium gallium arsenide. They can only be integrated into the silicon-based semiconductor technology, in the form of complicated and expensive hybrid processes. Such processes are not given any chances of use.
Silicon has long not been viewed as a suitable base material for light emitters because silicon, in contrast to for example gallium arsenide and many other semiconductor materials, is what is referred to as an indirect semiconductor. In the case of indirect semiconductors the energy minimum of the conduction band states, corresponding to the minimum energy of free electrons, and the energy maximum of the valence band states, corresponding to the minimum energy of free holes, considered as a function of the charge carrier pulse, is not at the same pulse value. As a photon is known to be practically pulse-free pulse production in terms of radiant recombination of free electron-hole pairs must be ensured in silicon by an interaction of the charge carriers with the crystal lattice, more specifically by the production of pulse-affected lattice waves in the form of one of more phonons. The annihilation of a free electron-hole pair with the emission of light therefore requires in silicon the production of a phonon in addition to the desired photon. Such a process has a lower level of probability than the direct production alone of a photon, as occurs in what are referred to as direct semiconductors such as gallium arsenide, in respect of which the energy minima of electrons and holes fall on the same pulse value.
Nonetheless recently efficient silicon-based light-emitters which rely on band-band recombination have been developed, see for example the present applicants' DE 10 2004 042 997 which was not yet published at the filing date of the present patent application.
For optoelectronic use however in particular light emitters in the spectral window around 1.5 μm (about 0.8 eV) or in the spectral window around 1.3 μm (about 0.94 eV) are required. Those spectral regions can be achieved when involving a radiant band-band recombination only with a silicon-germanium alloy with a high proportion of germanium. The low level of defects required for the necessary light yield however can only be implemented with difficulty when using such alloys.
Alternative approaches therefore involve “cultivating” known low-energy light emissions of silicon, which in accordance with the present day state of knowledge, are to be attributed to crystal defects such as dislocations. As the energy levels involved in the light emission are localized at the defects, the energy relaxation processes which lead to light emission can take place without phonon involvement.
The publication by V. Kveder, M. Badylevitch et al., “Room-temperature silicon light-emitting diodes based on dislocation luminescence”, Applied Physics Letters, volume 84, number 12, pages 2106-2108 discloses a light-emitting diode which at room temperature exhibits an electroluminescence which is dominated by what is referred to as the D1-line. D1-luminescence in silicon, in accordance with the view prevailing at the present time, is caused by radiant energy relaxation processes at dislocation structures, see T. Sekiguchi, S. Ito, A. Kanai, “Cathodoluminescence study on the tilt and twist boundaries in bonded silicon wafers”, Materials Science and Engineering B 91-92 (2002), pages 244-247.
V. Kveder et al. achieve an increase in the efficiency of D1-luminescence at room temperature by the suppression of non-radiant recombination processes which are caused by impurities localized in the surroundings of the dislocations.
A disadvantage of the light-emitting diodes described by Kveder et al. is that their luminescence extends over a relatively wide spectral range and also has a pronounced shoulder at higher energy levels around 0.85 eV. That luminescence is referred to as D2-luminescence. It is however of no interest for optoelectronic uses. The plastically deformed substrates used by Kveder et al. for the production of the light-emitting diodes also suffer from the disadvantage that the irregular dislocation arrangements contained therein, in accordance with the present state of the art, cannot be adequately reproducibly produced.